The Physiological Basis of Skin Conductance
Galvanic Skin Response (GSR), also known as Electrodermal Activity (EDA), is a non-invasive technique that quantifies the electrical characteristics of the skin. By detecting variations in the skin’s ability to conduct a small electrical current, researchers gain a window into an individual’s moment-to-moment physiological state.
The measurable electrical change results directly from the activity of eccrine sweat glands. These glands are densely concentrated on the palms of the hands and the soles of the feet. Unlike the apocrine glands involved in thermal regulation, eccrine glands respond primarily to mental and emotional states. When these glands become active, they secrete a small amount of moisture, which is an electrolyte solution.
This release of moisture onto the skin surface lowers the electrical resistance of the skin barrier. As the fluid fills the sweat ducts, the skin’s conductivity immediately increases. This physical process establishes a direct and measurable link between internal physiological mechanisms and the external electrical properties of the skin. The increased conductivity is what the GSR sensor registers and converts into a quantifiable signal, measured in microsiemens (µS).
Interpreting Arousal and Emotional State
The entire process of skin conductance is modulated by the sympathetic nervous system. This branch of the autonomic nervous system is responsible for the body’s rapid-response mobilization. Because this system operates automatically, GSR provides an objective measure of physiological arousal that cannot be intentionally influenced. The resulting conductance signal is therefore an unfiltered marker of internal activation.
Changes recorded in the GSR signal are widely interpreted as indicators of an individual’s level of emotional arousal, attention, and cognitive effort. When a person is exposed to novel, stressful, or emotionally charged stimuli, the sympathetic nervous system triggers the sweat glands, causing an immediate spike in skin conductance. This response reflects the body’s unconscious allocation of resources to process the incoming information or prepare for action.
It is important to understand that GSR measures the intensity of the emotional experience, not the specific type of emotion. A strong positive reaction, such as excitement, can produce a conductance spike identical in magnitude to a strong negative reaction, like fear or anxiety. Therefore, researchers rely on GSR to determine the overall level of emotional engagement or cognitive load, often combining it with other measures to infer the specific emotional context.
Practical Applications of GSR Testing
GSR testing has wide-ranging applications across multiple scientific and commercial fields due to its sensitivity as a marker of autonomic arousal. In psychological research, the technique is routinely used to study responses to various stimuli, including the investigation of phobias, anxiety disorders, and stress reactions. Researchers can precisely track the body’s unconscious response to specific images, sounds, or tasks to better understand the mechanisms of emotional processing.
The technology is also utilized in marketing and consumer neuroscience to gauge engagement with products, advertisements, or user interfaces. By measuring a person’s physiological arousal as they view a commercial, companies can objectively determine which parts of the content captured the most attention and generated the strongest emotional reaction. This provides data beyond what self-reported surveys or questionnaires can offer.
In a therapeutic context, GSR forms the basis of biofeedback training. Individuals learn to monitor and consciously regulate their own physiological stress responses. A patient watches their skin conductance readings in real-time and practices relaxation techniques to lower the signal, effectively learning to manage conditions like anxiety or chronic pain. GSR is also known for its historical use in polygraph testing, where skin conductance change is monitored as a component of the overall physiological stress profile.
The Process of Measurement
GSR measurement is conducted using a simple, non-invasive setup that employs two electrodes placed on the surface of the skin. The typical placement is on the fingertips or the palm, areas selected for their high concentration of eccrine sweat glands. The device then applies a very small, safe electrical voltage, usually around 0.5 volts, across the two electrodes to measure the resulting conductance.
The data generated from this process is analyzed in two distinct components. The Skin Conductance Level (SCL) represents the slowly changing, tonic background level of conductance, reflecting a person’s general or baseline state of arousal. The Skin Conductance Response (SCR) manifests as a rapid, transient spike in conductance that occurs almost immediately after a person is exposed to a specific stimulus. SCRs are the primary focus when investigating event-specific emotional reactions.